Solar Cell Splits Water for Hydrogen

Science has relentlessly sought nature’s ability to turn sunlight into useful fuel. Recently, Penn State University researchers developed a device that could split water and produce recoverable hydrogen.

“This is a proof-of-concept system that is very inefficient. But ultimately, catalytic systems with 10 to 15 percent solar conversion efficiency might be achievable,” said Thomas E. Mallouk, professor of materials, chemistry and physics at Penn State. If the system could be realized, it would provide a clean source of hydrogen fuel from water and sunlight.

Although solar cells can already produce electricity from visible light at efficiencies greater than 10 percent, solar hydrogen cells are theoretically better light absorbers because they can use more of the visible spectrum in a process much like natural photosynthesis.

Mallouk and W. Justin Youngblood, a postdoctoral fellow in chemistry, together with collaborators at Arizona State University, developed a catalyst system that, combined with a dye, can mimic photosynthesis.

Through this chemical process, the system splits water; however, the water splitting requires 1.23 volts. The current experimental configuration cannot quite achieve that level, so the researchers add about 0.3 volts from an outside source. Their current system achieves an efficiency of about 0.3 percent.

“Nature is only 1 to 3 percent efficient with photosynthesis,” Mallouk said, “which is why you cannot expect the clippings from your lawn to power your house and your car.”

The researchers have a variety of approaches to improve the process.

“At every branch in the process, there is a choice,” Mallouk said. “The question is how to get the electrons to stay in the proper path and not, for example, release their energy and go down to ground state without doing any work.”